The present invention relates to a device for measuring of compression forces, preferably compression forces acting on mine roof supports in an underground mine gallery, whereby the deformation of a pressure body composed of a plurality of cylindrical or straight prisms of different materials, or of the same materials, but of different dimensions, serves as indication of the compression force, and in which the pressure body is arranged between two pressure plates of a stronger material than that of the pressure body.
A plurality of measuring devices and processes are known, for measuring dynamic and static compression and tension forces, for instance for a weighing or dosing function, for testing the strength of materials or for indicating deformations on devices and constructions.
For instance in mines, the forces prevailing on a support of an underground mine gallery may be measured by means of pressure cells, known in the art, which are arranged between the support and the surrounding rock or between connected parts of the support. Such pressure cells are constituted by steel containers filled with liquid and closed at one end by a membrane, which is deformed if outer forces act on the container. The indicated liquid pressure is, at a central application of the force, a direct indication of the force acting at the support. A disadvantage of such pressure cells is that they are inaccurate if the pressure forces act on the cell in a direction inclined to the axis thereof. The pressure cells are even often damaged or destroyed, if the direction of the force acting on the cell deviates to a considerable extent from the direction of the axis thereof. This will produce inaccurate measuring results, respectively no measuring results at all. Another disadvantage of known pressure cells is that they are relatively complicated in construction and in addition relatively expensive, so that their use, especially in underground mine galleries, is further limited.
Another measuring device to be used underground, the so-called prop inserting press, which is described in the DT-Gbm 1,897,012 is only usable in certain cases, due to its considerable weight and the required high effort of operating personnel. Furthermore, this device is only suitable to determine momentary values of forces acting on individual props. A plurality of measurements at the same location and under different conditions is however not possible with this device. The prop inserting press is also not suitable for all support constructions, for instance not for arc-shaped supports in an underground mine gallery.
In the German DT-OS 21 06 193 pressure cells of rubber-elastic or similar material are described which are filled with a liquid or a gas. The indicated pressure can be read at a closed system on hydraulic or pneumatic pressure indicators or on sight glasses, or be determined in an open system by a measuring tube. Such devices are also suitable for inclined loading. Their production is, however, relatively complicated.
The use of conventional tension-expansion-measuring processes in underground mine galleries is for safety reasons often not applicable (limited permission of electric operating means in underground mine galleries) and the practical application of such measurements is further limited to a high degree due to the detrimental conditions in underground mine galleries (danger of corrosion by water or salts, detrimental influence of dust).
This is likewise applicable with respect to the known "force absorbers" which operate on the principle of the tension-elongation-measuring technique (see for instance the magazine "Materialpruefung 17" (1975, No. 8, page 302).
From the testing of material pressure bodies of metal of high tensile strengths and yield point (calot-measuring gauge) are known, which serve for the calibration of material testing machines. The elastic deformation of the body serves as indicator of the magnitude of the force. The amount of deformation can be mechanically determined by a dial gauge, by means of mirrors, or by a microscope, or be electrically determined by means of a capacitive or inductive arrangement. The practical use of such measuring devices in underground mine galleries is however connected with the same difficulties as already mentioned above.
Devices are further known from the DT-OS 21 06 192 in which deformations occurring at different locations of a pressure body are measured, which serve to indicate the forces applied thereto. The deformations may for instance be measured by slide gauges, whereby also inclined forces may be measured. A measuring device of the above-mentioned kind is also known in which the fracture of a pressure body of predetermined pressure resistance indicates surpassing of a load. A plurality of pressure bodies (disks), which are arranged parallel to each other and normal to the direction of the pressure force, and having different dimensions or different resistance against compression, permit a stepwise indication of the acting force. These small, light, easily manipulatable and also cheeply manufacturable measuring devices, which may be manufactured in large numbers and which are indifferent against explosions, dust, corrosion and temperature changes so as to satisfy the requirements of rough operation, to stand up under continuous load, and which are independent of any addition of energy (for instance electrical current, hydraulic) and which in addition due to their low price do not have to be recovered after the measuring process, have proven practical and usable especially for indicating of central forces. It has however been shown that, even though no high claim is usually placed in such measuring devices with respect to the exactness of the forces to be measured, these measuring devices are, especially for the determination of inclined acting forces, not very suitable.